Optical fiber communications systems are used extensively in the telecommunications industry due to their large information carrying capacity, their virtually noise-free performance, and the long span distances achievable with optical fibers before regeneration and amplification of the signal are required. Practical limits on the lengths of optical fiber cables that can be manufactured and installed typically require that several splice points be included over the total cable route.
At each such splice location, all of the optical fibers are separated from the other protective cable components for splicing and are, thus, more susceptible to damage. In addition, the optical fibers at a splice point are handled by a technician who splices the fibers and stores the splices and associated slack in a protective splice closure. In almost all fiber optic communications systems, it is critical that high quality and high reliability splices be obtained. Fusion and mechanical splicing techniques and equipment have been developed that permit low loss, high quality, and durable splices to be obtained. However, it may sometimes be necessary to remake or repair splices to achieve the desired splice quality.
There are many different types of splice closures for protecting optical fiber splices wherein all of the fibers are spliced to corresponding fibers in an adjacent cable section. Typically, these splice closures include one or more splice organizing trays, on which the individual splices and the relatively short lengths of associated slack fibers are mounted. For example, the assignee of the present invention manufactures a conventional splice enclosure and splice organizer under the model designation FOSC 100. Siecor Corporation of Hickory, N.C. makes splice enclosures under the model designations SC2, and SC4-6. Another splice enclosure is shown in UK Patent Application No. 2,150,313A assigned to Preformed Line Products of Cleveland, Ohio.
Another common fiber optic communication system application requiring fiber splicing includes a main cable serving several drop cables at spaced apart locations along the route of the main cable. Splices are required at these drop points; however, not all of the fibers in the main cable are severed and spliced. Rather, only a relatively small number of fibers are typically spliced to the drop cable. The remaining fibers, or express fibers, are desirably left undisturbed. Accordingly, a large amount of slack is typically associated with these express fibers. This slack may be in the form of a plurality of buffer tubes, each in turn containing a plurality of fibers.
Fiber optic splice closures have been developed for protecting the splices between a main cable and a drop cable. Such closures typically have an in-line arrangement of incoming and outgoing cables. In addition, such closures typically have a compartment for storing the relatively large amount of slack express fibers. For example, U.S. Pat. No. 4,805,979 to Bossard et al. entitled Fiber Optic Cable Splice Closure and assigned to 3M, discloses an in-line splice closure including two rigid half shells.
Unfortunately, the 3M splice closure is assembled by routing the slack buffer tubes in a compartment defined by the lower rigid shell, and the splice organizer trays and cable end attachments are built upon the bottom shell. Thus, initial assembly is somewhat complicated and, moreover, the slack is extremely difficult to reaccess once the closure is assembled as the bottom shell cannot be removed without substantially disassembling the entire splice closure.
U.S. Pat. No. 4,679,896 to Krafcik et al. entitled Optical Fiber Splice Organizer discloses a splice closure including a bottom slack storage tray positioned within a cylindrical housing. The slack stored in the tray may only be accessed after removing a series of stacked splice organizers from a pair of upwardly extending threaded studs. Stated in other words, the access opening for the slack storage tray is covered by the stacked splice organizers and access to the slack requires disturbing the splice trays.
Somewhat similar to the Krafcik et al. splice closure is the closure described in U.S. Pat. No. 4,428,645 to Korbelak et al. entitled Cable Accumulator. The splice closure includes a hinged and removable splice organizer and underlying compartment or tray for slack cable. The splice organizer must be pivoted out of the way to gain access to the slack storage compartment opening.
Similar to such conventional splice closures, is splice closure model FOSC 100.RTM.D manufactured by Raychem, assignee of the present invention. The FOSC 100.RTM.D includes as an option, a slack storage compartment that may be mounted underlying a series of pivotally secured splice organizing trays. The access opening for the slack storage compartment is covered by the splice organizing trays; however, the splice trays may be pivoted upward to gain access to the slack. Thus, the splice trays must still be repositioned to access the underlying slack.
There are other applications where conventional splice closures have significant shortcomings. For example, when a new drop point must be added to an existing or preinstalled main cable, a so-called "taut sheath" splice is desirable. Unfortunately, conventional splice closure, such as the 3M closure, may be too short to permit sufficient slack fibers to be exposed from the cable. Similarly, for a taut sheath ring splice, wherein both incoming and outgoing fibers are spliced to a drop cable, a conventional closure does not permit obtaining sufficient slack for splicing.
Another shortcoming of conventional splice closures is that the use of such closures is expensive for a typical repair of a severed cable, since two splice closures must be used. In other words, in a conventional repair, a patch length of slack cable is spliced to restore the damaged cable section and two splice closures are used to protect each of the splices to the patch cable ends.